An aerial bomb dropped by US troops during World War Two (WWII) was discovered in Upper Austria.Officials in the city of Linz said the 50-kilo bomb was found during construction work near the citys zoo this morning (Thurs). A special police force decided to evacuate everyone within a radius of 100 metres.The federal interior ministry assigned a team of explosives experts to examine and remove the aerial bomb. The missile was found to be harmless since its detonator turned out to be defect.US American and British army forces carried out dozens of aerial attacks on Austrian cities in the final years of WWII. Especially industrial estates in Linz and Wiener Neustadt, which is located south of Vienna, were targeted by the allied forces fighting the Third Reich regime of Adolf Hitler. Germany annexed Austria in March 1938. WWII broke out one and a half years later and ended in 1945.